Sinoracutine is a recently isolated alkaloid with unusual stereochemical and biological properties. It features an unprecedented tetracyclic 6/6/5/5 skeleton that bears an N-methylpyrrolidine ring fused to a cyclopentenone. Interestingly, both enantiomers of sinoracutine have been independently isolated from the same plant, yet the molecule does not appear to occur as a racemate. Here, we present a short synthesis of (-)-sinoracutine that relies on a highly diastereoselective Pauson-Khand reaction and a Mandai-Claisen reaction to install the quaternary stereocenter. Our work establishes the absolute configuration of the levorotatory isomer and suggests that the optical purity of sinoracutine varies in nature due to its gradual racemization. Experimental evidence supports this proposal, and a plausible mechanism for the racemization is provided.
The selectivea ddition of organomagnesium reagents to 2,4,6-trichlorophenyl isocyanide leading to magnesiated aldimines is reported. These aldimines reactw ith Weinreb amides, ketones, or carbonates to provide the corresponding carbonyl derivativesa fter acidic cleavage. This allows for an efficient synthesis of 1,2-dicarbonyl compoundsa nd a-hydroxy ketones.
Substituted arenes flanked by two bulky triethylsilyl groups were regiospecifically lithiated at the 5‐position with nBuLi⋅PMDTA at 25 °C. The resulting aryllithiums reacted with a broad range of electrophiles such as ketones, isocyanates, Weinreb amides, allyl bromides, and CO2 at 25 °C. These bis‐silylated arenes were then converted in simple reaction sequences into silyl‐free tetrasubstituted arenes. This remote lithiation was extended to 2,6‐bis(triethylsilyl)pyridine as well as 3,3′‐bis(triethylsilyl)biphenyl.
On the base of 2,2-bis(azidomethyl)propane-1,3-diol (BAMP) and 2,2-dinitropropane-1,3-diol (DNPD) four different polyurethanes were synthesized in a polyaddition reaction using hexamethylene diisocyanate (HMDI) and diisocyanato ethane (DIE). The obtained prepolymers were mainly characterized using vibrational spectroscopy (IR) and elemental analysis. For determination of low and high temperature behavior, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used. Investigations concerning friction and impact sensitivities were carried out using a BAM drop hammer and friction tester. The energetic properties of the polymers were determined using bomb calorimetric measurements and calculated with the EXPLO5 V6.02 computer code. The obtained values were compared with the glycidyl azide polymer (GAP). The compounds turned out to be insensitive toward friction (>360 N) and less sensitive toward impact (40 J)
Functionalized arenes bearing two bulky triethylsilyl substituents were regioselectively lithiated at the 4-position (para position) by using a mixture of nBuLi and PMDTA (N,N,N′,N ′′,N′′-pentamethyldiethylenetriamine). The resulting aryllithium species, bearing sensitive functional groups such as amides or carbamates, reacted with a range of electrophiles leading to tri- and tetrasubstituted remote-functionalized products. This lithiation could be extended to 2,2′-bis(triethylsilyl)biphenyl, for which the favored metalation site was the one where steric interference of the silyl group could be avoided.
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